SpaceX’s Dragon returns to Earth with precious cargo from ISS

October 28, 2012 by Pete Harding

SpaceX’s Dragon spacecraft has completed its trip back to Earth, carrying with it a valuable load of cargo from its host since October 10, the International Space Station. While the re-entry and splashdown of the Dragon was significant in itself – as it will be only the third time that a Dragon has performed this feat – it also marked the first significant return of cargo from the ISS since the landing of the final Space Shuttle on July 21, 2011.

Since then, Dragon has spent the past two weeks and four days – its longest ever flight – berthed to the ISS at the Node 2 Nadir Common Berthing Mechanism (CBM) port, while the crew of Expedition 33 unloaded around 880 pounds/400 kilograms of cargo from the Dragon, and loaded in its place nearly 1,700 pounds/760 kilograms of return cargo, or “downmass”, including valuable scientific samples and failed ISS hardware.

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Following the conclusion of cargo loading operations, the CBM hatch of the Dragon spacecraft was closed yesterday, following which the Atmosphere Revitalisation System (ARS) hose, two 1553 data cables, and two power jumpers were demated between the ISS and Dragon via the CBM vestibule.

The four CBM Controller Panel Assemblies (CPAs), box-like items that control the berthing sequence, were then installed on the ISS side, and finally the CBM Center Disk Cover (CDC) was installed prior to ISS hatch closure and depressurisation of the CBM vestibule.

For landing day, the long sequence of events that will ultimately lead to Dragon safely bobbing the Pacific Ocean began with the unberthing of Dragon from the Node 2 Nadir CBM, via the release of 16 bolts around the CBM berthing collar on the ISS side, performed in four sets of four bolts to ensure even unloading on the CBM interface.

Once complete, the ISS crew “pulled” Dragon away from the ISS via the use of the Space Station Remote Manipulator System (SSRMS) – which grappled Dragon on Wednesday – controlled from the Robotic Workstation (RWS) in the panoramic-viewed Cupola. Dragon was then be manouvered to the release position approximately 30 feet below the ISS.

Once in the release position, the time came for Dragon and the ISS to part ways, with ISS Commander Suni Williams squeezing the trigger on the Rotational Hand Controller (RHC) on the RWS to release the snares holding the SSRMS Latching End Effector (LEE) to the Dragon Flight Releasable Grapple Fixture (FRGF) – effectively “letting go” of Dragon. This process began on schedule at 1:26 PM GMT.

Dragon then completed its free-fly on-orbit after around five hours, during which time it completed a critical action – closure of the GNC bay door, to which the FRGF is mounted – before conducting a de-orbit burn at 6:28 PM GMT. The umbilical between Dragon and its Trunk then disengaged, prior to the Trunk separating from the Dragon capsule.

Entry Interface (EI) followed shortly thereafter, with Dragon making its fiery plunge through the atmosphere, protected by its PICA-X heat shield, which is designed to withstand off-nominal re-entries from Mars.

Following deployment of the three parachutes, Dragon was observed to have splashed down in the Pacific Ocean off the coast of California at 7:22 PM GMT.

Immediately following splashdown, a team of recovery personnel will begin making their way toward Dragon aboard a small outboard-motor powered boat, following which one member of the recovery team will climb atop the gently bobbing Dragon and attach a harness, whereupon a larger barge will arrive with a crane to lift Dragon out of the water via the harness, and place it on a purpose-built support base aboard the barge.

The process to open Dragon’s side hatch will then immediately commence, in order to remove high-priority, time-critical return cargo and get it back to NASA within 48 hours of splashdown, a capability demonstrated on the previous Dragon splashdown on May 31.

Dragon and its remaining cargo will then make its way back to the Port of Los Angeles via the barge, following which Dragon will be trucked to SpaceX’s facility in McGregor, Texas, where its remaining cargo will be unloaded and transferred to NASA’s Johnson Space Center (JSC), which will conclude the objectives of the CRS-1 mission and officially usher in the CRS era.

Since that time, valuable return cargo items have been piling up aboard the ISS, including scientific samples, failed hardware, and other no longer needed but still valuable/re-usable items such as spacesuit gloves for previous ISS crewmembers.

The ability to once again return these items will replace a significant capability lost with the retirement of the Space Shuttle, and enable increased scientific utilisation of the ISS.

On the scientific side, Dragon will be carrying a GLACIER freezer for entry and landing – as it was for launch – that will be filled with numerous scientific samples stockpiled since July 2011, including astronaut’s urine and blood samples that need to be analysed on Earth as part of on-going crew medical experiments and data gathering activities (for instance, urine can be analysed for calcium levels to give an indication of bone loss in microgravity).

These time-critical samples were loaded aboard Dragon yesterday, just prior to hatch closure, with the GLACIER freezer being transferred from an ISS ExPrESS Rack (ER) to the Dragon.

Several additional samples were placed in Double Cold Bags (DCBs). These frozen samples are the time-critical items that must be retrieved from Dragon immediately following splashdown, in order to prevent them from thawing out.

From the non-scientific perspective, Dragon adds a unique capability to return failed hardware, not just to repair and re-launch it (and thus save the cost of building new hardware), but also to aid in failure investigations as to why the hardware failed in the first place, in order to improve designs for future space vehicles – effectively turning every ISS hardware failure into a gold mine of data for spacecraft designers.

Notable failed hardware items aboard Dragon – which, like the science samples, have been awaiting a ride home to Earth for some time – are the Urine Monitoring System (UMS), which launched to the ISS on STS-135 but experienced issues during installation, a Catalytic Reactor (CR) from the Water Recovery System (WRS), a Fluids Control Pump Assembly (FCPA), an Electronic Unit (EU) from a MELFI freezer, a Camera Light Pan/tilt Assembly (CLPA) that was removed from the SSRMS during US EVA-19 in early September, and an ATV cabin fan.

Dragon’s next flight:

The CRS-2 Dragon flight – AKA SpX-2 – was discussed briefly on Friday during a NASA overview briefing for an upcoming US spacewalk on the ISS. ISS Program Manager Mike “Suff” Suffredini provided an update on the status of the CRS-2 mission in light of the “rapid unplanned disassembly” of a Falcon 9 engine during the launch of CRS-1.

While the CRS-2 flight was previously planned for January 2013, this date may now slip to the right due to the delayed Falcon 9 first stage shipment to Florida; although a January launch date is not critical from an ISS logistics standpoint.

The delay, however, may have knock-on effects for the CRS-3 (SpX-3) flight, as that flight will use the new Falcon 9 1.1 booster, and so modifications must be made to SpaceX’s SLC-40 launch pad between the CRS-2 and CRS-3 launches, as well as launches for customers other than NASA. Thus, any delay to the CRS-2 flight is likely to delay that modification work from occurring.

Suffredini added however that a NASA team are lending their experience to help SpaceX determine the root cause of the engine failure, and that the ISS is in good shape to cope with any delays, due to a good stockpile of logistics aboard the station.